1. Field of the Invention
The present invention relates to a method of and an apparatus for transferring a substrate from a take-up position to a specified position.
2. Description of the Related Art
In the manufacture of, for example, liquid crystal displays, a plurality of glass substrates used for manufacturing liquid crystal displays are stored in a cassette in a stacked manner and are conveyed to any one of manufacturing units by the cassette.
Each of the manufacturing units has a transferring apparatus and a processing section. The transferring apparatus is designed to transfer the glass substrates, one by one, form the cassette to the processing section. The transferring apparatus comprises a cassette mount region on which the transported cassette is placed so that the glass substrates in the cassette are located at a predetermined take-up position, and transferring means for taking out the glass substrates, one by one, from the cassette on the cassette mount region and transferring it to a specified transfer position which is suitable to the processing section.
Generally, the cassette is large enough to allow each glass substrate to move into and out of the cassette, with its sides not contacting the inner walls of the cassette, even if the transferring means moves sideways while transferring the substrate from the cassette. Thus, each glass substrate in the cassette may be displaced when the cassette is vibrated or inclined while the cassette is being moved from one manufacturing unit to another.
The transferring means moves between two fixed positions, that is, between the take-up position and the transfer position and transfers the glass substrate along a fixed path. Therefore, if a glass substrate is stored in the cassette with being displaced from a predetermined take-up position, this glass substrate is transferred by the transferring means from the cassette to the transfer position while maintaining the displaced state. Accordingly, the transferred glass substrate is located at a position displaced from the specified transfer position.
In order to solve the above-mentioned problem, there is provided a transferring apparatus which has a positioning mechanism for setting glass substrates in a desired position in a cassette placed on the cassette mount region. The mechanism has two pairs of positioning plates, each pair of which opposes each other. The positioning plates are moved toward the center of the glass substrate from outside so as to force the side edges of the substrate, thereby positioning the substrate in the desired take-up position. By positioning the glass substrate at the take-up position, the substrate can be accurately transferred to the transfer position.
However, the positioning mechanism applies an impact to the glass substrate since the plates mechanically push the four side edges of the glass substrate stored in the cassette. Applied with an impact, the glass substrate may have micro-cracks or may be chipped. Particularly, when the thickness of the glass substrate is smaller than 1 mm, micro-cracks increases.
Here arise two problems. First, dust is generated when micro-cracks are made in the glass substrate or when the glass substrate is chipped. The dust causes decrease in the yield of the manufacturing of the liquid crystal displays. Second, thermal stress concentrates at the micro-cracks or at a chipped part when the glass substrate is heated and cooled in another manufacturing processes, and the substrate may be broken.
If glass substrates repeatedly receive impacts, each time at the transferring apparatus of each manufacturing unit, they may therefore be broken at last, even if they have no micro-cracks or chipped parts at all.